Question

How does the internal energy (U) of a system change when heat flows into the system from the surroundings and work is done by the system on the surroundings.

a) More information is needed.

b) internal energy (U) decrease.

c) Internal energy (U) increases.

d) There is no change in the internal energy (U).

Answer 1

Answer: d) There is no change in the internal energy (U).

dQ = dU + dW

dU = dQ - dW

dU = (heat flows into the system from the surroundings) - (work is done by the system on the surroundings)

heat energy is given to system so internal energy increases, but at the same time work is done by the system on the surroundings so the same amount of internal energy decreases. The net reult is zero. The first law of thermodynamics relates changes in internal energy to heat added to a system and the work done by a system. The first law is simply a conservation of energy. It is like a thermal equilibrium state.

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